The present invention relates to a process for controlling a starting of a motor vehicle drive that has a driving engine and a starting device, using the quantities: the position of a power control element of the driving engine; the input rotational speed of the starting device, and the output rotational speed of the starting device, with the starting operation being carried out in two phases.
Generally, starting devices are devices which, in the case of vehicle drives, permit a starting of the vehicle. These include, for example, the known types of rotational speed converters (input and output speed differ; input and output torque are identical), such as friction clutches, magnetic clutches and magnetic particle clutches as well as hydrodynamic (converter) clutches. In this case, vehicle drives are particularly those drives which supply a usable torque only starting at a rotational speed larger than zero and therefore cannot be started in a rigid coupling to the device to be driven. The range above this rotational speed is called the power range; the range below it is called the starting range or the starting gap.
From German Patent Document DE-32 09 645 A1, an arrangement has become known for controlling a motor vehicle drive unit, in which a control unit controls an actuating drive of a hydraulic clutch in such a manner that the torque at the clutch is proportional to a pilot control value and proportional to the square of the rotational engine speed. The pilot control value is obtained via a characteristic curve converter from the signal of an accelerator pedal generator. The signal of the rotational speed generator controls via a second characteristic curve converter at the same time the throttle valve and thus the engine torque of the motor vehicle drive unit.
Furthermore, from German Patent Document DE 36 06 229 A1, a device is known for automatically controlling the start of an engine-driven vehicle which is used for automatically engaging a friction clutch corresponding to the actuating of an accelerator pedal. For this purpose, the position of the accelerator pedal is sensed, and a first control device affecting the engine holds the rotational engine speed on a desired rotational speed which was determined as a function of the position of the accelerator pedal. A second control device affecting the clutch controls the slip of the clutch for a predetermined time period corresponding to characteristic data which are also selected as a function of the position of the accelerator pedal.
It is an object of the invention to provide an arrangement and a process for controlling a starting device which is improved, on the one hand, while taking into account the driver's wishes and, on the other hand, while taking into account the vehicle environment.
This and other objects are achieved by the present invention which provides a process for controlling a starting of a motor vehicle drive that has a driving engine and a starting device, and comprises the steps of using the quantities: position of a power control element of the driving engine; the input rotational speed of the starting device, and the output rotational speed of the starting device; and carrying out a starting operation in two phases. These phases include a first phase in which the input rotational speed is led to a desired rotational speed, and a subsequent second phase in which a rotational speed difference signal formed from the difference between the input rotational speed and the output rotational speed is led along a desired course to the zero value.
The objects are also achieved by another embodiment of the present invention which provides a control arrangement for a driving engine and a starting device connected behind it, comprising a first generator for outputting a position of a power control element of the driving engine, a second generator for outputting an input rotational speed signal of the starting device, and a third generator for outputting an output rotational speed signal of the starting device 2. A difference forming device is coupled to the second and third generators and determines a rotational speed difference signal as the difference between the input rotational speed signal and the output rotational speed signal. A first characteristic curve converter is coupled to the first generator for determining a desired rotational speed as a function of the signal of the first generator. A first control device is provided which, in a first phase of the starting operation, generates a difference actuating signal in such a manner that the input rotational speed signal is led to the desired rotational speed signal and in a second phase, generates the difference actuating signal in such a manner that the rotational speed difference signal changes at a rate which is a function of the size of the rotational speed difference signal. A second characteristic curve converter is coupled to the first generator for determining a first actuating signal as a function of the position of the power control element, the input rotational speed signal and the desired rotational speed. A second control device determines a second actuating signal from the first actuating signal and an application actuating signal. An actuating device acts upon the starting device according to the sum of the second actuating signal and the difference actuating signal.
It is particularly advantageous that the starting dynamics and the agility are improved by the present invention without any cutbacks with respect to the parking comfort. At the same time, the starting device is treated with better care, is protected from misuse by means of overloading and is securely saved from destruction. For this purpose, the starting operation is carried out in two phases, specifically in a first phase in which the rotational input speed is led to a desired rotational speed and, in a second subsequent phase, in which a rotational speed difference signal formed from the difference between the rotational input speed and the rotational output speed is caused to follow a predetermined desired course to the zero value. As a result of the invention, the starting behavior is a function of changes of the conditions at the starting device which may occur, for example, as the result of stress and wear.
It is suggested to let the first phase begin when the starting device is not completely closed and the position of the power control element is below a limit value. As a result, each starting operation will be recognized irrespective of whether it is a start from a stopped condition or a restart after a deceleration condition that is not quite a stoppage. Within the first phase and as a function of the position of the power control element, of the time variation of the position of the power control element and a signal describing the driver's driving style, the desired rotational speed is determined first and is therefore adapted to the driver's driving style or his driving wish. While the driving style is sensed for an extended period of time and therefore, during the first start, after the start-up of the vehicle, is still at its basic value, the starting operation can clearly be influenced by the power control element, in which case, in addition to the absolute position, the speed is also taken into account at which the power control element was brought to it. Subsequently, by means of the thus determined desired rotational speed, a desired curve of a control signal for an actuator of the starting device is determined in such a manner that in the actual position of the power control element, this desired rotational speed will definitely be reached. Thus, it is taken into account that, based on the rotational idling speed, not every desired rotational speed can be reached along the same path, that is, along the same characteristic curve. Finally, and this is where the actual starting operation begins, via the characteristic curve and as a function of the position of the power control element and the input rotational speed signal, the actuating device is controlled by the control signal in such a manner that the input rotational speed signal approaches the desired rotational speed.
For the second phase of the starting operation, this second phase begins when the input rotational speed signal has almost reached the desired rotational speed. In order to also take cases into account in which acceleration takes place only slowly and at a constant power, it is also provided to begin the second phase in every case when a predetermined driving speed is reached. In the second phase, a rotational speed difference signal--that is, the slip existing in the starting device, is led toward zero according to a desired curve. The speed at which the rotational speed difference signal is changed according to this desired curve is, in turn, a function of the rotational speed difference signal and becomes continuously lower the lower the rotational speed difference signal. Because of the desired curve, which operates by the return of the rotational speed difference signal in a closed control circuit, this second phase is not affected by outside influences, such as temperature and wear. The course of the desired curve and therefore the starting comfort can be adjusted within wide ranges. As a result of the suggested course of the desired curve, a very comfortable engaging of the clutch, for example, is possible because in the proximity of the clutch engaging point the input and the output rotational speed signals are caused to approach one another more and more slowly and therefore without any jerking. This transition between an almost closed and a completely closed starting device therefore takes place without any disturbing jerky transitions.
The observation of the thermal stress to the clutch is necessary in order to be able to recognize a threatening thermal destruction in time. For this purpose, it is suggested that a stress value be determined which represents the utilization of the stressing capacity of the starting device utilized up to then and by means of which the starting operation can be influenced. In the event of stress, the stress value is determined by calculating the frictional output occurring in the clutch, and in the case of a reduction of stress, it is determined by means of a cooling function. According to the present invention, the starting operation is carried out as a function of the utilization of the stressing capacity of the starting device and a sudden reaching or exceeding of the stressing limit is therefore avoided. The influencing of the starting operation takes place in a particularly simple manner by a determination of the desired rotational speed which is a function of the stress value, particularly by a lowering of the desired rotational speed with a rising stress value.
Certain embodiments of the invention provide measures which are used under special circumstances independently or in addition to the above-described measures in order to improve the overall operation of the starting device under any conceivable conditions. Thus, in a case in which the stress limit of the starting device could be reached or even exceeded, it is provided that the driver be informed of it, in which event, in addition to the exceeding of the stress limit, the amount of the still remaining stress reserve is indicated beforehand. Furthermore, measures are provided by means of which the start of a coasting of the vehicle is improved when the starting device must be opened up because the stress limit is reached. As a result, the driver will prevent unexpected reactions of the vehicle.
In order to minimize the influence of wear, temperature, aging, etc. of the starting device as well as the influence of the actuator acting upon the starting device on the starting operation, measures are indicated for determining a system actuating signal. This system actuating system is always determined again in such a manner that, when the actuator is acted upon by this signal, the starting device is operated close to the engaging or slip point so that, with a further increase of the signal, the starting device begins to grip immediately. In this case, the indicated process for determining the system actuating signal is distinguished by a particularly rugged method of operation under all operating conditions.
Furthermore, in certain embodiments, to securely open up the starting device under certain conditions, for example, when the vehicle is stopped, the actuating signal is reduced by a predetermined amount in order to thus minimize the stressing of the starting device and to prevent a crawling of the vehicle.
In addition, in certain embodiments under certain conditions, for example, after the stoppage of a vehicle or after a preceding (negative) control pulse, a (positive) control pulse is emitted by means of which empty runs existing in the starting device are overcome and therefore the system actuating signal is reached again as fast as possible in the actuator in order to again initiate a gripping of the starting device as soon as possible and to be able to react faster to a starting command of the driver.
By means of the automatic closing of the starting device when the vehicle starts to roll without any power demand, as for example, on a gradient, the braking effect of the engine is maintained.
Finally, certain embodiments of the invention provide measures by which the efficiency of the engine is utilized to the largest possible extent for the acceleration of the vehicle. It is particularly advantageous in this case that these measures are taken only in response to a special demand signal and that therefore an unintentional use and misuse can be prevented.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.